GitLab

This CL: 
- eliminates unnecessary dispatches
- correctly handles devices that are discovered before interest is
registered

TEST=ran api test
BUG=133179


Review URL: https://chromiumcodereview.appspot.com/10815072

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150898 0039d316-1c4b-4281-b951-d872f2087c98